1. Field of the Invention
The present invention relates to a method for manufacturing parts, and especially of large bulk, by means of powder injection molding or PIM techniques, using so-called hybrid feedstocks containing short or long inorganic fibres or nanofibres.
More specifically, such inorganic fibres or nanofibres may be made of carbon, metal, or ceramic. They are added during the PIM process and disappear at the end of the process, either by dissociation to form an alloy (in the case of a fibre of a different material than the part) or by dissolution in the material (in the case of a fibre of same material as the part).
The components manufactured by means of a method according to the invention provide remarkable properties at all manufacturing steps. Indeed:                the injected parts have an improved mechanical behavior;        the debound parts have an improved mechanical behavior;        the sintered parts have unequaled functional properties, especially improved mechanical properties, density, and heat conductivity.        
2. Desription of Related Art
The use of fibres or nanofibres as additives in plastics engineering (polymer manufacturing industry) is known in many industrial applications such as the automobile, aeronautical, and medical fields. The resulting materials, formed of fibres embedded in a polymer matrix, are called polymer-matrix composites.
Such materials more generally have the following properties, which derive from the addition of fibres:                mechanical strengthening;        shock absorption;        high elastic moduli;        fire retardant.        
In this context, and more generally, the added fibre is a glass polyaramid (Kevlar®), carbon, or aramid fibre.
Further, the PIM process is currently used to manufacture small metal or ceramic components. Generally, the parts are rather small (bulk of a few cm3) and have a complex shape, since it is a replication process.
In practice, powder injection molding (PIM) is a method which however has a number of disadvantages, which currently appear to be inseparable from this technology, having the following recurrent defects:                the parts are not dense after sintering (a few residual porosities approximately between 1 and 10%), which induces a degradation of functional properties: low heat conductivity, low mechanical properties, low wear resistance . . . , as described in document “Microstructure and mechanical properties of titanium components fabricated by a new powder injection molding technique” (Eric Nyberg, Megan Miller, Kevin Simmons and K. Scott Weila, Materials Science and Engineering C 25 (2005) 336 - 342).        the parts are very brittle when green, that is, just after injection, and when debound.        
The brittleness of PIM parts is a recurrent subject, which has been the object of many recent publications, such as document EP 1972419. These problems however have no real technical solution to date.
In this technical field, the use of fibres or nanofibres in feedstocks to manufacture metal matrix composites (MMC) has been mentioned in the past. The fibre is then only used to strengthen the final product, as is the case in an MMC. Thus, and in all cases, fibres have no interest for intermediate steps, especially at the debinding step, and are only used to provide specific properties, generally mechanical, to the final component which is thus formed of fibres embedded in the matrix.
A very thorough description of the state of the art in relation with the MIM (Metal Injection Molding) technique is provided in the following article: Hezhou Ye, Xing Yang Liu, Hanpring Hong, Journal of Materials processing Technology 200 (2008) 12-24.
There thus is an obvious need for the development of new technical solutions, enabling to avoid the pitfalls mentioned hereabove in relation with the PIM technology, and this, at the different steps of the process, and especially at the debinding.